Conductive materials are often applied to a circuit board substrate using the screen printing technique. A conductive paste, which can contain, for example, silver, aluminum or conductive carbon black, is applied to a substrate to produce a conductor on the substrate. Applications are also known in which similar conductive printing methods are applied to a printing substrate in a lithographic printing method.
One of the possible applications is the so called radio frequency identification (RFID) tags. These RFID tags present the possibility of storing data on a product. The stored data can be used, for example, to control product streams and simplify the management of inventories. Because of the clearly higher data storage capacity compared to the known bar code decoding, RFID tags can conceivably have any number of additional application fields.
A RFID tag consists of an antenna, optionally additional electronic components, and the RFID chip, which is typically applied using the so called bonding method. Today, antennas of the RFID tags can be applied without a problem by offset printing, screen printing or flexoprinting, while the chips needed for the RFID tags are generally glued or soldered to the contact places of the antenna. However, it is conceivable that in the future complete electronic circuits will be printed on a printed product. The antennas can be designed as a coil or a dipole antenna, depending on the frequency band used.
However, the printed antennas can interfere with the desired visual design of the printed package, because of the color hue of the conductive printing inks and its relatively high layer density, which is required to achieve good conductivity of the seams. In addition, the RFID tag which is printed on the exterior of a package can be destroyed or removed easily. An additional problem arises if, in a later processing step, the chip is glued or soldered to the contact place of the antenna. During the adhesive process or soldering process, heat is often generated at the adhesion places, causing discoloration of the printing substrate or, in a worse case, burns on the printing substrate. The discoloration or burns are not desired if only because they interfere with the decorative appearance of the packages.